The fuel cell system comprises at least one fuel cell, preferably a stack of multiple fuel cells, and a cathode recirculation channel. The fuel cell has a cathode side and an anode side. At the cathode side a cathode inlet for supplying an oxidant fluid to the fuel cell and a cathode outlet for discharging a cathode product fluid from the fuel cell is provided. The oxidant fluid may preferably be an oxygenic gas, such as air, or pure oxygen. The cathode product fluid represents the reaction product of the chemical reaction in the fuel cell at the cathode side and is usually a gas. At the anode side an anode inlet for supplying a fuel fluid to the fuel cell and an anode outlet for discharging an anode product fluid from the fuel cell is provided. The fuel fluid may preferably be a hydrogenous gas or pure hydrogen. The anode product fluid represents the reaction product of the chemical reaction in the fuel cell at the anode side and is usually a gas. The cathode recirculation channel connects the cathode outlet to the cathode inlet for passing the cathode product fluid from the cathode outlet to the cathode inlet to be used as an oxidant fluid fed into the fuel cell.
Such fuel cell systems are known in the prior art. DE 10 2005 010 399 A1 describes a fuel cell system as an emergency power supply comprising a stack of fuel cells connected to an oxidant supply and a hydrogen supply, a pump, and a converter unit. DE 10 2012 002 131 A1 discloses an emergency supply system comprising a fuel cell system and a fire fighting system, the fuel cell system comprises a fuel cell, an oxygen supply and a hydrogen supply for supplying oxygen and hydrogen to the fuel cell. Further, the fuel cell has an outlet for discharging a product gas from the fuel cell. The outlet is connected to the fire fighting system for passing oxygen depleted air as a product from the chemical reaction in the fuel cell from the outlet of the fuel cell to the fire fighting system in order to be used as a fire suppression media. From the fire fighting system the remaining oxygen depleted air is recirculated through a recirculation channel and fed into an inlet of the fuel cell.
However, when the product fluid with the oxygen depleted air is recirculated and fed into the fuel cell again as a reactant, and this recirculation process is repeated several times, the water content in the product fluid increases continuously which decreases efficiency of the fuel cell system and eventually may block the entire fuel cell system.